Added Merge Sort #77

MergeSort.cpp

@@ -0,0 +1,98 @@
+// C++ program for Merge Sort
+#include <iostream>
+using namespace std;
+
+// Merges two subarrays of arr[].
+// First subarray is arr[l..m]
+// Second subarray is arr[m+1..r]
+void merge(int arr[], int l, int m, int r)
+{
+	int n1 = m - l + 1;
+	int n2 = r - m;
+
+	// Create temp arrays
+	int L[n1], R[n2];
+
+	// Copy data to temp arrays L[] and R[]
+	for (int i = 0; i < n1; i++)
+		L[i] = arr[l + i];
+	for (int j = 0; j < n2; j++)
+		R[j] = arr[m + 1 + j];
+
+	// Merge the temp arrays back into arr[l..r]
+
+	// Initial index of first subarray
+	int i = 0;
+
+	// Initial index of second subarray
+	int j = 0;
+
+	// Initial index of merged subarray
+	int k = l;
+
+	while (i < n1 && j < n2) {
+		if (L[i] <= R[j]) {
+			arr[k] = L[i];
+			i++;
+		}
+		else {
+			arr[k] = R[j];
+			j++;
+		}
+		k++;
+	}
+
+	// Copy the remaining elements of
+	// L[], if there are any
+	while (i < n1) {
+		arr[k] = L[i];
+		i++;
+		k++;
+	}
+
+	// Copy the remaining elements of
+	// R[], if there are any
+	while (j < n2) {
+		arr[k] = R[j];
+		j++;
+		k++;
+	}
+}
+
+// l is for left index and r is
+// right index of the sub-array
+// of arr to be sorted */
+void mergeSort(int arr[],int l,int r){
+	if(l>=r){
+		return;//returns recursively
+	}
+	int m =l+ (r-l)/2;
+	mergeSort(arr,l,m);
+	mergeSort(arr,m+1,r);
+	merge(arr,l,m,r);
+}
+
+// UTILITY FUNCTIONS
+// Function to print an array
+void printArray(int A[], int size)
+{
+	for (int i = 0; i < size; i++)
+		cout << A[i] << " ";
+}
+
+// Driver code
+int main()
+{
+	int arr[] = { 12, 11, 13, 5, 6, 7 };
+	int arr_size = sizeof(arr) / sizeof(arr[0]);
+
+	cout << "Given array is \n";
+	printArray(arr, arr_size);
+
+	mergeSort(arr, 0, arr_size - 1);
+
+	cout << "\nSorted array is \n";
+	printArray(arr, arr_size);
+	return 0;
+}
+